We are limited in our ability to recognize and treat lethal forms of prostate and other cancers by an incomplete understanding of the biological mechanisms that govern cell proliferation, or of the derangements in these mechanisms that permit pathological proliferation within the primary organ and at metastatic sites. In our recent studies in the mouse we have discovered a signal feedback circuit between epithelium and stroma that appears to be a central control mechanism governing proliferative activity in urogenital organs. We propose to test the role of this epithelial/stromal circuit, particularly a supportive stromal response, in the control of cell proliferation in bladder and prostate and in malignancies of these urogenital organs. We discovered this control circuit by examining the dramatic proliferative response to bladder injury caused by infection with uropathogenic bacteria. Upon infection, expression of the Sonic hedgehog (Shh) protein signal increases in a subset of basal cells of the urothelium, and this triggers a response in cells of the underlying stroma, including increased expression of Wnt and FGF secreted protein signals; consequently, epithelial and stromal cells undergo a dramatic and sustained increase in proliferation. The key to uncovering this control circuit was our finding that Gli1, a Shh transcriptional effector dispensable for embryonic development, nevertheless appears to play a critical role in post-embryonic proliferative responses. We have found that proliferation in the prostate, despite a striking hormonal dependence that is absent in bladder, also appears to employ Gli1, suggesting a proliferation control mechanism similar to that of the bladder. We propose to test the role of signaling pathways in this proliferative control circuit in murine bladder and prostate and to investigate the activity of this circuit in urogenital malignancies. We will use bacterial infection of the bladder and testosterone replacement in castrates as triggers for regenerative proliferation responses, and will delineate the signaling pathways that mediate epithelial/stromal signaling using tissue microdissection and microarray gene expression analysis. Functional studies will make use of genetic analysis and pharmacological agents. We will investigate the role of this proliferative control circuit in malignancies of urogenital organs using mouse models, human cancer cell lines, and the large Stanford collection of cryopreserved human tumor tissues. Our focus in these studies will be on the supportive response of stromal cells as a critical factor in fostering growth and specifying the likelihood of distant metastases. Our studies will provide new diagnostic and therapeutic approaches to urogenital malignancies by improving our ability to recognize cancers with metastatic potential and by testing the effects of FDA-approved pharmacological agents recently found to potently modulate activities of the Hh and Wnt signaling pathways. Our findings thus will contribute directly to a base of knowledge that can be used to rapidly design and implement new clinical trials.